impossible,the inspire doesnt know what height its at, the displayed altitude is loosely based on the difference from current position vs where it took off from, it has no idea of actual altitude above sea level or altitude of the terrain at its current position. Change altitude a few times during flight and youll notice the displayed altitude is different even when the inspire is in the same spot. you dont have to "set" anything, you can fly wherever you want at whatever altitude you want up to 1640feet from the take off position unless youre using beginner mode where you can set max height, if thats the case I suggest you switch to normal mode and use common sense, then you dont have to worry about setting anything if you fly around mountains/valleys with terrain height changing drastically. If youre in the middle of nowhere and not interfering with any other aircraft the 400ft rule is basically a guideline and no one is gonna care or report you if youre flying from a mountain/valley situation and exceed that limit even if youre not in the middle of nowhere unless you fly close to manned aircraft perhaps, if anyone even sees you which is unlikely.